It is common to program robots to perform routine and repetitive tasks in manufacturing. One such task is the deburring of the edges of machined or cast parts. A robotic arm may be fitted with a deburring tool and programmed to follow a path around the edge of a particular part or object which is to be deburred.
There are some difficulties normally associated with the use of robotically controlled deburring tools. Since the programmed path of the robotic arm is in essence a series of incremental steps, the path of the robotically controlled deburring tool does not exactly coincide with the shape or contours of the surface to be deburred. In addition, the edge or surface may have cavities within the surface or even protrusions, sometimes prevalent in castings, extending from the surface to be deburred. These pockets and protrusions interfere with the path and cutting force of the robotic tool. A protrusion will urge the cutting surface of the deburring tool out of its programmed path and cause a consequent increase in cutting force. The increased cutting force may cause the deburring tool to cut too deep into the surface. Moreover, the increased cutting force may cause damage to the cutting surface of the tool. A cavity on the other hand may cause the deburring tool to separate or diverge from the surface to be machined. The separation of the cutting surface of the tool from the surface to be deburred will prevent the deburring of that portion of the part or workpiece. Consequently, the overall quality of the product being deburred will be affected.
In addition to part variations, there are fixture variations. Fixtures are structures that hold the parts while the parts are being subjected to deburring. Fixtures are designed to hold the parts such that the surface to be deburred aligns with the programmed path of the deburring tool. However, typically, these fixtures will have variations, and the variations will result in the surfaces of the parts to be deburred being misaligned with the programmed path of the deburring tool.
Traditionally, these problems have been dealt with by designing expensive and complicated active compliance whereby sophisticated electronic controls manipulate the robotic arm. Compliance compensates for errors in the path and variations in parts and fixtures by permitting limited movement of the tool while maintaining an acceptable cutting force. In this way, variations in the surface being deburred or inaccuracies in the programmed path which are within the limits of the compliance will be accommodated and damage to the cutting surface of the tool and the finished product will be minimized.
Several types of compliant tool holders have been disclosed in the prior art. In U.S. Pat. No. 4,637,775 entitled “Industrial Robot Device,” compliance is provided by a spring built into the device holding the tool. The spring permits the tool, which is comprised of the cutting surface and the drive means for the cutting surface, to move laterally relative to the axis of the tool and away from the edge being deburred. In U.S. Pat. No. 4,860,500 entitled “Passive Actuator to Maintain a Constant Normal Cutting Force During Robotic Deburring,” an air cylinder with a low friction piston is used to provide a zero spring rate compliance. Here the cutting surface and the drive means of the tool are permitted to move laterally to accommodate path errors and surface variations. Further, it is known to provide compliance devices in robotic deburring tools. For example, there is commercially available a robotic deburring tool known as Amtru Flexicut 240 which is manufactured in Switzerland. This robotic deburring tool includes an air motor disposed within a housing. The air motor includes a rear or back portion that lies within a ring-type compliance device while the front portion of the air motor extends through a mounting structure that permits the front portion of the motor to pivot. The pneumatic motor in the Amtru Flexicut deburring tool is relatively large, and because of that the entire tool is relatively heavy, bulky and expensive.